Demonstration of Ellipse Definition Small 320×266 Medium 640×531 Large 1024×850 Download Tiff Original 2400×1992 | (238.0 KB) Description Illustration showing the definition of an ellipse. "An ellipse is a curve which is the locus of a point that moves in a plane so that the sum of its distances from two fixed points in the plane is constant." The foci and major axis is drawn. Keywords conic sections, definition, ellipse, ellipses, foci, focus, major axis, minor axis, oval, ovals, section Galleries Conic Sections: Ellipses Source: G.A. Wentworth Plane And Solid Geometry (Boston: Ginn & Company, 1899) 425 Courtesy the private collection of Roy Winkelman